— It's two dollars.

Fred likes fish very much. One day, he buys(买)some fish and takes it home. His son sees the fish and says to himself, "Very good! I can ask my friends to have it for lunch. "

The next day(第二天), Fred comes back home in the evening. The fish isn't there. His son says, "Oh, Dad, your cat eats the fish." Fred gets angry(生气). He takes the cat and his son to the shop and weighs(称)the cat. Then he says, "Little boy, my fish weighs one kilo, and the cat weighs one kilo too. My fish is here, then where is my cat?"